The research observed mothers' activity levels over 45 years. The information came from the American Heritage Time Use Study, which tracks how moms spend their time outside of employment.
The study reveals that in 2010 mothers of children between ages five and 18 spent 11 fewer hours doing physical activities, such as laundry and exercise, than mothers in 1965.
Mothers of kids less than five-years-old spent 14 fewer hours doing physical activities than their past counterparts.
According to the study, modern moms may be using that extra time to do more stationary tasks, such as watching television.
Moms of older children spent seven more hours doing less-strenuous tasks, like driving, than moms did in 1965.
Today's moms raising kids under five increased their sedentary time by six hours over past moms.
Moms of younger kids went from spending 27 more hours a week participating in physical activity than inactive activity in 1965 to just doing seven more hours a week engaging in physical rather than inactive activity.
The authors of the study notice that the decline in physical tasks may be contributing to the country's obesity problem.
Government estimates show that more than one-third of U.S. adults are obese.
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